Not used a lot of these on bikes. But, I have on cars with drum brakes. My findings:
Stock pads were asbestos. These would fade with heat and water ingress. And, the drum would wear slowly.
I learned about Velvatouch Linings. These were sintered metal. Touted as having no speed fade, no heat fade, and no water fade. I put these on a 55 Chevy, a 61 ford galaxie, and a 65 Mustang. True to advertising, brakes were very good and performed WAY better than stock asbestos, no speed fade, no heat fade, and no water fade. I once did repeated acceleration to 60 and max brake to 10 MPH 10 times in a row in that 55 Chev. Brakes were always there, but smelled funny. I got out to see the drums glowing red and the paint on the rims was burning/ blistering off. I was impressed. It was explained that, that asbestos linings don't conduct heat very well through the lining. All the dissipation must go to the outside of the drum. But, with metallics, heat could dissipate into the shoe backing as well. I know for a while NASCAR was using Ceramic shoes, on drum brakes, for both heat dissipation and part survival to keep the shoes from welding to the drum using metallic linings.
The down side of metallic linings is that they do wear out the drums faster, sometimes you can get brake squeal, and if the brakes are put away wet, and allowed to sit, they can rust to the drums. So when driving in rain, I do several hard stops before parking to heat them up some and vaporize the water.
Velvatouch went out of business in the 80's, I think. But, I found a brake shop that relined truck shoes with metallic linings on your old shoes. I put these on a a 61 Chrysler, and my 72 Ford F-100. I liked them and while not as easy to service as Disc brakes, served well and always have good braking qualities. The only drum brake vehicle I have left is the Truck. Still has the metalic linings on it. I've towed trailers up and down mountains with it, and was thrilled to always have full braking whenever needed, especially on 6% down hills.
So, on to the SOHC4 bikes. I don't know what the material the stock pads are made of, but they do have metal bits embedded. My take is that the more metal you have in the pads, the more aggressive the braking/friction can be. I have tried SBC sintered bronze pads. But, the horrible brake squeal that developed had me going back to the stock ones.
Something to consider, is that if you are doing repeated heavy braking with metallic pads, remember they conduct heat into the piston cavity. Dot 3 has some temperature limits that might not be compatible, and 5.1 might be a better choice if you plan to use the brakes like on a race track. And of course, the higher the metallic density of the pad, the faster the disc is going to wear out. Lastly I expect the pads with the most metal will have less speed fade, heat fade, and water fade than pads with lower metal content.
As to stopping power, with a change in pad only, I found that dumping the expando rubber hydraulic lines in favor of SS lines, gave me a rock hard lever, and allowed the stock pads and disc to squeal the front tire on heavy braking with lot's of hand pressure. I really don't want to lock the front tire, as with just about any lean angle, a front tire lock will mean going down pretty quick. I equate tire squeal with being on the limit of traction. And I don't mind using four fingers to get that instead of the one or two finger squeeze of the the lever modern bikes have. (of course, you can get used to it. But then, going back is an issue) If I could have put up with the squeal, the bronze pads did require a bit less squeeze pressure for the same braking effort. I didn't run them long enough to notice how much more disc wear there was.
Hope this helps you make a good decision for your needs.
Cheers,
